Detection of a corrugated velocity pattern in the spiral galaxy NGC 5427

Here we report the detection, in H alpha emission, of a radial corrugation in the velocity field of the spiral galaxy NGC 5427. The central velocity of the H alpha line displays coherent, wavy-like variations in the vicinity of the spiral arms. The spectra along three different arm segments show that the maximum amplitude of the sinusoidal line variations are displaced some 500 pc from the central part of the spiral arms. The peak blueshifted velocities appear some 500 pc upstream of the arm, whereas the peak red-shifted velocities are located some 500 pc downstream of the arm. This kinematical behavior is similar to the one expected in a galactic bore generated by the interaction of a spiral density wave with a thick gaseous disk, as recently modeled by Martos & Cox.